In engines provided with a plurality of intake ports for one combustion chamber, the intake ports may for example be branched in the cylinder head, a fuel injector may be provided immediately before the branch, and fuel sprayed toward the branch.
With this kind of system, however, much of the fuel sprayed collides with the walls of the intake ports, and tends to set up a liquid wall flow along the walls. As this wall flow reaches the combustion chamber later than the vaporized fuel, the air-fuel ratio (AFR) is rendered unstable and engine running performance declines.
To improve this situation, Jikkai Sho 60-97373 and Jikkai Sho 63-132876 published by the Japanese Patent Office disclose a fuel injector having a fuel injection outlet pointing towards each intake port.
In this case, fuel is sprayed toward every port, and wall flow is therefore less. However, even in this fuel injector, there is a small distance from the outlet situated just before the branch and the intake valve, and it is therefore impossible to avoid some of the fuel being deposited on the wall of the port or on the stem of the intake valve which opens and closes the port before it reaches the chamber.
In another method of preventing wall flow, Tokkai Sho 63-106357, Jikkai Hei 1-118159 and Jikkai Shoe 64-11364 published by the Japanese Patent Office disclose a structure wherein fuel and air are mixed in the injector to promote conversion of fuel to fine droplets and mixing.
In this system, fuel is injected from a valve in the injector, and the mixture of this fuel with air aspirated into the fuel injector is delivered by a guide pipe close to the intake valve where is it expelled.
In this fuel injector, wall flow in the intake port is completely prevented. However, the guide pipe from the fuel injector body leads close to the intake valve, and in an engine provided with a plurality of intake ports for each cylinder as described hereintofore, fuel can be supplied to only one port. It was therefore difficult to overcome the problem of unevenness of fuel density in the combustion chamber.